dark mode for apple mail message body Redux

I have dark mode selected. In Mail Settings on the View tab I have selected Use Dark Background for Messages. I still see messages with white backgroun ds. I can use browser to see those emails with Dark backgrounds using the right browser extension. is this not possible in the mail app?

If I cannot fix, this, the use of the mail app is too unpleasant to use. I will continue to use web email apps.

Alan